Add wallabag docker deployment role

Added role of wallabag. Can take a subdomain alias to be presented on a
different uri than its stack name.

All services contain a healthcheck for docker swarm to be informed of
their status.

Copy whoami template to wallabag role

Change non-domain domain name to localhost

Fix correct handler notify naming

Allow setting different subdomain alias than name

Add meta information

roles/wallabag/defaults/main.yml

@@ -0,0 +1,10 @@
+---
+
+wallabag_version: latest
+
+wallabag_upstream_file_dir: "{{ docker_stack_files_dir }}/{{ stack.name }}"
+
+wallabag_use_https: true
+
+# the subdomain link wallabag will be reachable under
+subdomain_alias: read